The present invention relates to a method and an apparatus for controlling friction between the leaf springs of a laminated leaf spring assembly in accordance with the state of a body to be supported.
A laminated leaf spring assembly including a number of leaf springs has been widely used for suspending a body to be supported, for example, the body of a vehicle. When the laminated leaf spring assembly is used for suspending the vehicle, the comfort, the driving stability and the like are influenced by the spring constant, the friction between the leaf springs of the assembly and the like. The degree of such influence depends on the vehicle speed, the condition of the road surface and the like. In general, when the vehicle runs on a smooth road, the smaller the friction acting on the opposing surfaces of each pair of adjacent leaf springs, that is, the friction between the leaf springs, the better becomes the comfort. On the other hand, a higher driving stability is attained when the friction between the leaf springs is large. The comfort is considered to be more important than the driving stability on the smooth road, since sufficient driving stability is ensured if a steering wheel is not suddenly turned.
A laminated leaf spring assembly including a number of tapered leaf springs has been proposed. The tapered leaf springs are decreased in thickness toward the ends. The weight of the laminated leaf spring assembly including such a construction is smaller than that including leaf springs of the constant thickness since the number of the former may be smaller than that of the latter. If the number of the leaf springs is smaller than that of the prior art laminated leaf spring assembly, the friction between the leaf springs is reduced. As a result, a shock absorber of a large capacity is required to improve the comfort on a rough road. However, such a shock absorber of a large capacity is expensive. In addition, the comfort is sometimes impaired, since the shock absorber provides constant damping even if the damping is not needed. Therefore, clamping means is used for clamping the leaf springs near the ends thereof in the direction of their thickness to increase the friction between the leaf springs. The conventional clamping means securely clamps the leaf springs by bolts. As a result, the friction between the leaf springs is maintained at a large value so that the comfort on the rough road is improved. However, the comfort on the smooth road is unsatisfactory.